There aren't many places you'll find Nine Inch Nails, Bob Dylan, Peter Gabriel and Perry Farrell hanging out together, except maybe on a Mudstock reunion tour. Or on a movie soundtrack, also featuring, say, Jello Biafra, the Cowboy Junkies, the ghost of Patsy Cline and ... oh, what the hell, Snoop Doggy Dogg and Dr. Dre.

All of those acts are part of the wildly disparate musical lineup on the 27-cut, hot-selling soundtrack issued for "Natural Born Killers," the latest cinematic knuckle sandwich from director Oliver Stone. The movie is plenty frightening, and so is hearing actress Juliette Lewis moaning "Born Bad" and Nine Inch Nails frontman Trent Reznor howling "Burn."

Those who grew up in an era when a movie soundtrack meant the artistic unity of "Saturday Night Fever," "The Big Chill" or "Dirty Dancing" probably wonder why anyone would possibly buy the "Natural Born Killers" soundtrack. If you've been keeping up with music in the '90s, though, you might be among the 400,000 people who rushed to own this mind-bending compilation, which represents not only what's new about soundtracks but also how they have changed the music biz.

Today's soundtracks, like yesteryear's, are vehicles for possible hits. But now they move more units than ever, providing a phenomenal string of sales successes in the past two years: "The Bodyguard" (11 million), "Sleepless in Seattle" (3 million), "Above the Rim" (2 million), "Reality Bites" (2 million), "Boomerang" (2 million), "Singles," "The Crow" and "Philadelphia" (1 million each). "The Lion King," at 6 million sold, is currently the top album in the country, and "Forrest Gump," a two-CD oldies compilation that's sold 2.5 million copies in a matter of weeks, is No. 2.

Increasingly, soundtracks serve as hype-wagons for movies themselves. A good track can help promote a film before it opens and extend its run at the box office. Video clips from singles released off the soundtrack become mini-trailers -- for example, Elton John's "Can You Feel the Love Tonight," which got heavy VH1 play and provided a preview of "The Lion King" animation. Sometimes, as in the case of "Above the Rim" or "Reality Bites," a soundtrack can provide unexpected revenues for a studio that watches its movie sink quickly at the box office.

"There's no doubt that a soundtrack provides exposure," says Budd Carr, executive producer of the "Natural Born Killers" soundtrack, whose songs are beginning to get airplay on radio. "And everyone today needs multiple format exposure."

Carr has worked on finding music for 40 films, beginning with 1984's "The Terminator." "There is more clout in the soundtrack today," he says, "and so much more music to choose from. You can do a low-budget picture these days and find great artists who are dying to get their stuff in the picture."

Just about every movie released has a soundtrack of some sort, whether it's original music composed for the film (officially called scores, these are generally not huge sellers); specially written songs or newly recorded tunes pitched to film directors and soundtrack producers; or oldies that are dusted off to provide period atmosphere. There's even a totally new beast, the soundtrack "inspired by" a movie, which means the music on the CD wasn't really in the picture, but somebody saw a way to possibly make a buck. (Take, please, "Songs From and Inspired by the Motion Picture 'Speed,' " a haphazard collision of a bunch of car- and driving-themed songs.)

Soundtracks merge the best and worst traits of Hollywood: hyper-marketing meets visionary artistry, very often resulting in dubious product. (Did the world really need a "My Girl 2" soundtrack?) CDs are relatively cheap to produce, and the "Soundtrack" bin at the record store is overflowing. The upcoming Sharon Stone-Sylvester Stallone coupling "The Specialist" will spawn an unprecedented three soundtracks: a score, music from the motion picture and an album of remixed dance tracks.

Glen Brunman, senior vice president of Epic Soundtrax, who produced the soundtracks for "Sleepless in Seattle," "Singles," "Philadelphia" and "The Specialist," puts it this way:

"When record companies see that some tracks are selling a lot of copies, everyone gets to get into the act. And when movie companies see what a soundtrack can do, they say, 'Hey, we can make money! We can enhance the success of the movie!' Inevitably, when something works, you can end up with excess. Yes, there are too many soundtracks being done, but who's to say which one is gonna work and which isn't?"

No one could have predicted, for example, that Lisa Loeb's pouty, angular tune "Stay (I Missed You)," tacked onto the end credits of the Gen-X film "Reality Bites," would reach No. 1 this summer. Loeb, who happened to be a neighbor of "Bites" star Ethan Hawke, got on the soundtrack by sheer coincidence; she didn't have a recording deal, but Hawke knew and liked her music.

Another example of serendipity: When Mary Stuart Masterson was preparing for her role in 1993's "Benny & Joon," she repeatedly played "I'm Gonna Be (500 Miles)," a crush-anthem released in 1988 by the Scottish duo the Proclaimers. It ended up as the film's signature song, and became a hit. But U.S. radio wouldn't touch "500 Miles" in 1988, and never would have in 1993 had it not been for callers demanding it after seeing the film.

A good soundtrack is more than an aural souvenir of the movie; it's like a good mix tape lovingly made by a friend with a truly inspired record collection. It exposes you to new music from unexpected sources. This is especially important as commercial radio becomes more genre-bound; unlike radio programmers, soundtracks allow competing tastes to coexist.

"Today's music buyer is interested in finding new things," says "Killers" music producer Budd Carr. "And people certainly have the opportunity to do that through this soundtrack. It wasn't calculated to be commercial. Putting Patsy Cline and the Dogg Pound on the same record is doing something different."

Though opposites in approach, the "Killers" and "Forrest Gump" albums provide a good example of how soundtracks are compiled today. Both demonstrate an overarching artistic vision that began with the movie director but allowed for strong input from musicians. That both products are successful is not only the result of the strength of movies ("Gump" is No. 1 at the box office, "Killers" No. 2); it also speaks to the public appetite for music of all kinds.

Despite relying on oldies beloved by baby boomers -- among them classic tracks by Jefferson Airplane, the Doors and the Four Tops -- "Gump" is selling surprisingly well among teenagers. "We all sell consumers short -- we just think they want what they like and what they live with," says Brunman. "If you expose people to great songs, even if they don't know them, they will respond. That is really the lesson of 'Sleepless in Seattle' and 'Forrest Gump.' "

"Sleepless" was basically a compilation of director Nora Ephron's favorite "make-out music" from when she was growing up in the '50s, Brunman says, yet standards by Jimmy Durante and Nat King Cole struck a chord with listeners of all ages. The music became a vital, if sometimes intrusive, character in the movie.

That's also true of "Gump." The movie features pieces of 58 songs -- culled from an estimated 5,000 potential numbers considered by executive music producer Joel Sill, whose soundtrack experience dates to 1969's "Easy Rider." As Forrest moves through 30 years of history, the songs act as literal time markers in the script. Thirty-one selections -- all by American artists -- ended up on the two soundtrack CDs.

Representatives of bands whose songs were being licensed were shown rough cuts of the movie to ensure that they concurred with the placement. In the case of the Doors, who have five songs in the movie, this was a contract requirement. But more often it was a courtesy to the musicians, as song licensing rights are frequently controlled by music publishers or other third parties.

Sill wasn't able to get rights to at least one song that he wanted: "The Candy Man" by Sammy Davis Jr. The rights, he said, turned out to be controlled by the Mars Candy Co. So the soundtrack producers subbed in B.J. Thomas's "Raindrops Keep Falling on My Head."

One song was ultimately scrapped from the picture because it had the wrong "tone," says Sill. "In the Nixon resignation sequence, we talked about using Crosby, Stills, Nash & Young's 'Ohio.' But the sentiment is so strong, and using that over Nixon's image just hammers him." Instead, the movie ended up using "Tie a Yellow Ribbon" to score a Nixon sequence.

The "Natural Born Killers" soundtrack also has its share of oldies, but hardly the shopworn fare of Classic Rock stations. Its tone is as primal, fringy and gut-clenching as the motion picture. The movie was essentially scored by Trent Reznor, who took computer equipment and a rough cut on the road and worked on the music for three months while touring. Using a pastiche approach, Reznor interwove movie dialogue, sound effects and splices from about 135 different songs. The pared-down CD was hailed by the Los Angeles Times as "a soundtrack like no other."

The CD includes three punishing NIN tracks and two by dirge-master Leonard Cohen. L7, Patti Smith and Jane's Addiction offer their own special beams of happy sunshine. Another heavy hand in the mix is LA rapper Dr. Dre, who's produced hits for Snoop Doggy Dogg. Dre was invited to an early screening of "Killers" and invited to suggest songs.

"We are getting better opportunities as music supervisors to go to {musical} artists and tell them, 'Here are the characters, here are the scenes, here is what the movie's about,' and let them become part of the creative process," says Carr, who's worked on director Stone's soundtracks since "Salvador" (1986).

"Once Oliver decided there would be no composer for the picture, I listened to 10 CDs a day, from producers, record labels and music publishers," says Carr. Among them were songs pitched by the adventuresome Mute label, which represents British soundscape composer Barry Adamson and New York performance artist Diamanda Galas. Both ended up on the soundtrack CD, giving hope of wider public attention to their obscure work.

In the main, though, the public still savors soundtracks that provide the accessible commercial pap that has always been a big part of the movie-going experience: the inevitable, overblown signature tunes like "Up Where We Belong" or "Wind Beneath My Wings" or "I Will Always Love You." Out in Hollywood, music supervisors are busy coming up with the perfect song for "Love Affair," the remake of "An Affair to Remember," the 1957 weeper that was key to the success of "Sleepless in Seattle."

Vic Damone did the honors in the original, and this time it's likely to be somebody in the schmaltz tradition. What, you were expecting Snoop Doggy Dogg?